Stabilization of bleach baths of high alkalinity



NOV. 1943- J. CAMPBELL ETAL 2,333,916

STABILIZATION OF BLEACH BATHS OF HIGH ALKALINITY Filed Sept. 25, 1940 soA 5 1.

8 12 16 BLEACHING TIME IN HOURS Z 9c E U) a E v .L 2 (I) 9 O O U LU n- OU I 9; D28 [n n: 5 2 AM 0 "L186 Lu m 2 Zn. I 3 m0 S l; n: I 84 g 2 D i.-5. I g 82 Z -2 AMOUNT OF STABILIZING AGENT IN 1 3 1 GRAMS PER LITER OFBLEACH BATH Z1 /2 /4 3 VOLUME CONCENTRATION E OF BLEACH BATH INVENTORS.DONALD J. CAMPBELL E 2 WILLIAM LOFTUS m T A TTRNE.

Patented Nov. 9, 1943 STABILIZATION OF BLEACH RATES OF HIGH ALKALINITYDonald J. Campbell and William H. Loftus, Niagara Falls, N. Y.,assignors to E. I. du Pont de Nemours & Company, Wilmington, DeL, a

corporation of Delaware Application September 25, 1940, Serial No.358,318

Claims.

This invention relates to the stabilization of bleach baths comprisingaqueous solutions of peroxygen compounds. More particularly, it relatesto the stabilization of bleach baths of relatively high alkalinity suchas those resulting from the dissolution of alkali metal peroxides inwater or from the preparation of solutions of inorganic peroxides suchas hydrogen peroxide containing relatively large amounts ofunneutralized alkali.

Unneutralized aqueous solutions of alkali metal peroxides, such asunneutralized aqueous solutions of sodium peroxide, have been used to alimited extent for the bleaching of cotton materials. These solutionsare prepared by-dissolving a commercial alkali metal peroxide, such asthe sodium peroxide sold under the trade mark name Solozone, in water orsimilar aqueous liquid without the introduction of acid or acidicsubstances for purposes of regulating the pH of the bleaching bath.While this is the most convenient way of preparing solutions ofinorganic peroxides containing relatively large quantities of dissolvedalkali, such solutions can of course also be prepared by introducingfairly large amounts of alkaline agents into an aqueous solution ofhydrogen peroxide.

While solutions of inorganic peroxides containing fairly large amountsof dissolved alkali have been successfully employed in the bleaching oftextile goods such as cotton, such baths, by reason of their relativelyhigh content of dissolved alkali, have been relatively unstable, evenwhen maintained at relatively low temperatures such as thosecorresponding to room temperature or below. This invention isparticularly directed to new and improved stabilizers for stabilizingsuch solutions of inorganic peroxides of relatively high dissolvedalkali content.

One object of this invention may be said to involve the stabilization ofbleach baths comprising inorganic peroxygen compounds, which bleachbaths are of relatively high pH and contain considerable quantities ofunneutralized al kali. An ancillary object of our invention is theutilization of a mixed stabilizer comprising magnesium sulfate andsodium pyrophosphate in combination, for stabilizing solutions ofinorganic peroxides containing fairly large amounts of alkali per liter,such as solutions resulting from the dissolution in water of alkalimetal peroxides without the addition of sufficient acids or acidmaterials to neutralize the alkali metal hydroxide formed. These andfurther objects of our invention will be apparent from the ensuingdisclosure of certain preferred embodiments thereof.

The solution of inorganic peroxide which it is a primary object of thisinvention to stabilize are those having pH values of 11.5 or above. Suchsolutions may be prepared by dissolving an alkali metal peroxide such assodium peroxide in water, the quantity of sodium peroxide added being atleast 0.75 pound per 100 gallons of bleach bath, and there beingintroduced into said solution no acid or acid substance for the purposeof neutralizing or partially neutralizing any of the sodium hydroxideformed as a result of the dissolution of the sodium peroxide in water.They may also be prepared from solutions of other inorganic peroxidessuch as hydrogen peroxide by introducing thereinto sufiicient of analkaline material such as caustic soda or soda ash to yield a solutionhaving a pH of 11.5 or above. The

amount of alkali thus introduced will be at least equivalent to thatproduced by dissolving 0.75 pound of sodium peroxide per gallons ofbleach liquor without any neutralization or partial neutralization bythe addition of acids or acid substances.

We have found that when baths of the specified high alkalinity, having apH of 11.5 or above, are stabilized by the addition thereto Of a mixedstabilizer comprising magnesium sulfate and sodium pyrophosphate, theresults are much more satisfactory than when either stabilizer isutilized alone. This mixed stabilizer is more satisfactory than anyother stabilizer that we have investi gated in the course of our studyof the Problem of stabilizing solutions of inorganic peroxides of highalkali content. We prefer to use the ordinary commercial magnesiumsulfate, magnesium sulfate heptahydrate, MgSOflI-IzO (Epsom salts), andtetrasodium pyrophosphate, Na4PzOv, although the crystalline salt,sodium pyrophosphate decahydrate, Na4Pz0m10H2O, is equally suitable. Ofcourse the use of the hydrated salts is not essential, and anhydrousmagnesium sulfate may be utilized with equal success. In place of thesodium pyrophosphate, other alkali metal pyrophosphates may be used,although, by reason of its relative cheapness and ready availability, weprefer to utilize sodium pyrophosphate decahydrate. In place of themagnesium sulfate any soluble magnesium salt such as magnesium chloridemay be used with equally satisfactory results. For purposes ofconvenience, however, our invention will be described with particularreference to our preferred compounds, sodium pyrophosphate and magnesiumsulfate.

We have found that the ratio of the amount of sodium pyrophosphate tothe amount of magnesiu sulfate or other soluble magnesium salt in thestabilizer may vary within certain limits.

Thus, the mixed stabilizer may consist of one part by weight ofmagnesium sulfate heptahydrate and as little as two or three parts byweight of sodium pyrophosphate decahydrate. Ratios of sodiumpyrophosphate to magnesium sulfate in excess of three to one will, undersome circumstances, be found to yield slightly better stabilizingaction. When the ratio of the salts comprising the stabilizing agent isone part by weight 7 of magnesium sulfate heptahydrate to four parts byweight of sodium pyrophosphate decahydrate, the stabilizer functionsvery satisfactorily, and

very superior stabilization is secured up to a ratio of one part of themagnesium sulfate to seven parts by weight of the sodium pyrophosphate.With ratios'ranging from one part by weight of magnesium sulfate toseven parts by weight of sodium pyrophosphate, to one part by weight ofmagnesium sulfate to thirteen parts by weight of sodium pyrophosphate, ahigh degree of stabilizing action is secured, although stability of thesolutions'for equal quantities of the stabilizer may be somewhat lessthan that of solutions wherein stabilizers higher in ratio of magnesiumsulfate content to sodium pyrophosphate content are present.

We have found that the amount of stabilizer necessary to securesatisfactory stabilizing action is not unduly critical. Amounts of thestabilizer suflicient to introduce into the solution from 3 to 8 utilizeit in baths very much more concentrated than 1 volume, 1. e., containingmore than 6.0 pounds of sodium peroxide or any equivalent alkali contentper 100 gallons of bleach bath. It may here be noted thatthevconcentration of a peroxygen compound such as sodium peroxide orhydrogen peroxide in a bleach bath is frequently expressed in terms ofvolume concentration, one volume concentration being that concentrationof peroxygen compound yielding a solution which will release one volumeof oxygen gas, measured at 0 C. and 760 mm. of mercury pressure, fromone volume of the solution measured at C. when sodium peroxide isutilized as the peroxygen compound, a solution of 0.75 volumeconcentration corresponds substantially to one having dissolved therein4.5 pounds of sodium peroxide per 100 gallons of bleach liquor.Similarly, a solution of 0.50 volume corresponds to a. bath containingsubstantially 3.0 pounds of sodium peroxide per 100 gallons of bleachbath, while a bleach bath of 0.25 volume concentration will contain 1.50pounds of sodium peroxide per 100 gallons of bleach bath. We havesecured satisfactory stabflizing action with bleach baths as low as0.125 volume (equivalent to 0.75 pound of sodium peroxide per 100gallons of solution) or of even lower sodium peroxide concentration.Such baths will all have pH values of substantially 11.5 or above.

It may here be noted that commercial solutions of hydrogen peroxide,such as those sold under the trade-mark name Albone, are all of 100volume concentration, which is equivalent to 27.6% 11:02 by weight.

While our combined stabilizing agent, formed by utilizing magnesiumsulfate and sodium pyrophosphate conjointly, is entirely effective forstabilizing bleach baths of much higher alkali content than thatcorresponding to unneutralized sodiu peroxide of 1 volume concentration,with solutions of higher alkali content there is danger of precipitationof the magnesium. Thus, with bleach baths containing concentrations ofalkali higher than that corresponding to a 1 volume solution ofunneutralized sodium peroxide, there is a tendency for the bath tobecome somewhat turbid. With solutions containing an alkali contentequivalent to that produced by preparing a bath of 2 volumeconcentration by the use of unneutralized sodium peroxide (12 pounds ofsodium peroxide per gallons of bleach liquor) there is observed aflocculent precipitate. While the presence of this flocculentprecipitate is not necessarily objectionable and does not appear tointerfere with the stabilizing action of our new and improvedstabilizing agent, in bleach baths where clarity and the absence ofturbidity or a precipitate is important we prefer to utilize solutionshaving analkali content not over that corresponding to a bleach bath of1 volume concentration, prepared by the dissolution of unneutraiizedsodium peroxide.

It should be understood that in specifying the alkali content of theactive oxygen bleach baths the stabilization of which forms the objectof this invention, such baths may also be prepared in other ways than bydissolving an alkali metal peroxide such as sodium peroxide in waterwithout the addition of any acid or acid substance to effectneutralization. Thus, they may be prepared from solutions of hydrogenperoxide by dissolving alkaline agents such as caustic soda or soda ashtherein until the pH of the solution is 11.5 or above. Alternatively,they may be prepared by dissolving an alkali metal peroxide such assodium peroxide in amounts larger than those herein specified andintroducing greater or less amounts of acid to eflfect partialneutralization of the peroxide. The solutions whose stabilization formsthe object of this invention have pH values of 11.5 or higher andcontain a content of dissolved alkali at least equivalent to thatpresent in a bleach bath of unneutralized sodium peroxide of 0.125volume concentration, such a bath containing substantially 0.75 pound ofsodium peroxide per 100 gallons of bleach liquor.

In the annexed drawing various experimental results are plotted asgraphs to illustrate the remarkable effectiveness of sodiumpyrophosphate and magnesium sulfate when used conjointly for thestabilization of bleach baths of high alkali content. In the drawingFig. l is a graph wherein the bleaching time in hours is plotted againstthe percent of decomposition of the bleach bath. Fig. 2 shows thesuperior whiteness obtained at 50% decomposition of the bleach bath whenthe bleach bath is stabilized with our new and improved stabilizingagent, as compared with unstabilized bleach baths of equalconcentration. Fig. 3 is a graph showing the great superiority of sodiumpyrophosphate and magnesium sulfate when used conjointly for stabilizingbleach bathsof high alkali content over eitherv stabilizer when utilizedalone. This figure also illustrates the superiority of the new andimproved stabilizer over sodium silicate, an agent frequently utilizedas a stabilizer in commercial bleach baths.

Referring first to Fig. 1, the bleaching time in hours is plottedagainst the percent decomposition of the bleach bath. The bleach bathwas one of 0.5 volume concentration, produced by dissolving sodiumperoxide in an unneutralized bath in amount corresponding to 3 pounds ofthe peroxide per 100 gallons of bleach liquor. The bath was then usedfor bleaching cotton goods in accordance with the usual commercialprocedure at a temperature of 180 F., the amount of cotton goods beingequivalent substantially to 50 grams per liter of bleach liquor.

Curve A represents the graph of results obtained utilizing no stabilizerin the unneutralized sodium peroxide bleach bath. Curve B is the curveresulting when our improved stabilizer was utilized comprisingsubstantially one gram of magnesium sulfate heptahydrate and three grams'of sodium pyrophosphate decahydrate per liter of bleaching solution.

The remarkable stability of the bleach bath stabilized with ourstabilizer mixture is illustrated by the fact that over twenty-two hourswere required for 100% decomposition of the bleach bath at the highlyelevated temperature employed during the bleaching, contrasted with fourhours for the unstabilized bath. 7

We have also observed that for equal amounts of active oxygen thewhiteness of the resulting bleached cotton is greater when that cottonis bleached in baths stabilized with our stabilizer than it is when thecotton is bleached in unstabilized baths prepared by dissolvingunneutralized sodium peroxide in water. This fact is illustrated by thegraph comprising Fig. 2, wherein percentage of whiteness for 50%decomposition of the bleach bath is plotted against the volumeconcentration of various bleach baths formed of unneutralized sodiumperoxide and having volume concentrations up to 1 volume. In each casethe bath was used to bleach cotton which had been previously boiled outin accordance with the usual practice, the amount of cottoncorresponding approximately to 50 grams of cotton per liter of bleachliquor. On this graph, curve L is the curve resulting when theunneutralized sodium peroxide bleach bath is one that has beenstabilized by the use of our improved stabilizing agent, while curve Mrepresents the results secured with unstabilized bleach baths. It willbe apparent, for example, that when a bleach bath of volumeconcentration is utilized, bleached cotton of over 92% whiteness issecured by use of the stabilized bleach bath, as contrasted with cottonof only about 88% whiteness secured by the use of the unstabilized bath,The percentage whiteness values given on this graph are the whitenessvalues secured after 50% of the available peroxide present in the bleachbath has been consumed.

The superiority of our conjoint stabilizercomprising an alkali metalpyrophosphate and a soluble magnesium salt, sodium pyrophosphate andmagnesium sulfate being the preferred agents, for stabilizing bleachbaths of high alkali content is strikingly illustrated in the graph ofFig. 3. This graph resulted from tests with a bleach bath of 0.5 volumeconcentration prepared by dissolving unneutralized sodium peroxide inwater, the bath containing substantially 3 pounds of sodium peroxide per100 gallons of bleach liquor. The tests were carried out at 180 F. inthe presence of 50 grams per liter of cotton goods, these conditionsapproximating those encountered in commercial bleaching processes.

This curve shows the time required for 50% decomposition of the bleachbath plotted against various amounts of stabilizing agent. Thesestabilizing agents were as follows:

1. Sodium pyrophosphate alone (results shown on curve N).

2. Commercial sodium silicate of 42 B. concentration (results shown oncurve 0) 3. Magnesium sulfate and sodium silicate (results shown oncurve P).

' 4. Our new and improved stabilizer comprising sodium pyrophosphate andmagnesium sulfate (results shown on curve R).

In all cases except with our improved stabilizing agent, amounts up to10 grams of the stabilizer per liter of bleach liquor or more wereutilized. In the case of our improved stabilizer, by reason of theremarkable stability imparted to the solution by its use, it wasunnecessary to use amounts over 2 grams per liter.

It will be noted that there is very little to choose between stabilizersI, 2, and 3 above, plotted on curves N, O, and P. In all cases, evenwith amounts of stabilizer up to 10 grams per liter, 50% decompositionoccurred within about one hour or less. With our improved stabilizer itrequired twelve hours for 50% decomposition of the bleach bath to occurwhen only two grams per liter of the stabilizing agent was employed. Thesuperiority of our new agent, illustrated by curve R, is indeedremarkable when one considers the exceedingly elevated temperature atwhich the comparative bleaching trials were carried out.

We are of course aware that magnesium sulfate has previously beenutilized both alone and in combination with sodium silicate forstabilizing bleach baths comprising peroxygen compounds. Similarly,sodium pyrophosphate has been used alone for stabilizing such bleachbaths. It is in-- deed remarkable, however, that when utilizingconjointly magnesium sulfate and sodium pyrophosphate in bleach baths ofthe high alkali content with which this invention is concerned, havingpH values of 11.5 or above, there is obtained that very surprisingincrease in stabilizing action resulting from the conjoint use of thetwo salts. As illustrated by Fig. 3. the increased stabilizing action isvery much more than the sum of the stabilizing actions of the twoindividual components.

As an example of a bleaching process employing our new and improvedstabilized bleach baths the following may be given:

Example A bleach bath was prepared by dissolving 15 pounds of sodiumperoxide, 10 pounds of sodium pyrophosphate (Na4PzO-z.10HzO) and 5pounds of magnesium sulfate (MgSQ4.7I-I2O) in 700 gallons of bleachliquor. This bleach bath was then used to bleach 700 pounds of rawcotton stock in a commercial vacuum type iron bleaching machine.

The cotton bleached was given a preliminary boil-off in a solutioncontaining 20 pounds of soda ash per 700 gallons of solution. Theboil-ofl was continued for twenty minutes in accordance with the usualpre-treatment procedure, whereupon the cotton was thoroughly rinsed inwater for five minutes.

The boiled-out cotton was now introduced into the bleach bath maintainedat an elevated temperature by the application of steam, and bleachingcontinued for about two hours. At the end of this period the cotton wasbleached to a very high degree of whiteness and was in every respectsatisfactory. Fiuidity determinations were made upon samples of thecotton to determine degradation, and the percentage degradation wasfound to be well within allowable limits. Although an iron machine wasemployed during the bleaching, no sign of attack or corrosion on themetal of the machine was observable.

Those skilled in the art will appreciate that numerous changes,modifications and adaptations of our invention may be made withoutdeparting from its novel teachings. Thus, while our invention has beenparticularly described with reference to our preferred agents, sodiumpyrophosphate and magnesium sulfate, it should be understood that theuse of other alkali metal pyrophosphates and of other soluble magnesiumsalts is comprehended within its scope. and modifications as come withinthe scope of the appended claims are intended to be embraced therein.

We claim:

1. A stabilized bleach bath comprising an aqueous solution of aperoxygen compound having a pH of at least 11.5 and containing an alkalimetal pyrophosphate and a soluble magnesium salt as the stabilizingagent.

2. A stabilized bleach bath comprising an aqueous solution of aperoxygen compound having a pH of at least 11.5 and containing sodiumpyrophosphate and magnesium sulfate as the stabilizing agent.

3. A stabilized bleach bath comprising an aqueous solution of aninorganic peroxide having a pH of at least 11.5 and containing, as thestabilizing agent, sodium pyrophosphate and magnesium sulfate.

4. A stabilized bleach bath comprising an aque-.

least 11.5 and containing from 0.75 pound of sodium peroxide per 100gallons of bleach bath to 6.0 pounds of sodium peroxide per 100 gallonsof bleach bath, said solution containing no acidic constituentsintroduced f r the purpose of regulating the alkali content thereof, andcontaining as stabilizer therefor, sodium pyrophosphate and magnesiumsulfate.

8. A stabilized bleach bath having a pH of at least 11.5 and containingfrom 0.75 pound of sodium peroxide per 100 gallons of bleach bath to 6.0pounds of sodium peroxide per 100 gallons of bleach bath, said solutioncontaining no acidic All changes prises adding thereto sodiumpyrophosphate and magnesium sulfate.

10.The process of stabilizing a bleach bath comprising an unneutralizedsolution of an alkali metal peroxide having a pH of at least 11.5 whichcomprises adding thereto sodium pyrophosphate and magnesium sulfate.

11. The process of stabilizing a bleach bath comprising an unneutralizedsolution of an alkali metal peroxide which comprises adding thereto analkali metal pyrophosphate and a soluble mag nesium salt, the pH of saidsolution of alkali metal peroxide being at least 11.5,

12. The process of stabilizing a bleach bath comprising an alkalinesolution of hydrogen peroxide having a pH of at least 11.5 whichcomprises introducing thereinto, as stabilizing agent, sodiumpyrophosphate and magnesium sulfate.

13. The process of stabilizing a bleach bath Y comprising anunneutralized solution'of sodium peroxide having a pH of at least 11.5which comprises adding thereto sodium pyrophosphate and magnesiumsulfate.

14. The process of stabilizing a bleach bath comprising an unneutralizedsolution of an alkali metal peroxide containing at least 0.75 pound ofsodium peroxide per gallons of bleach liquor which comprises addingthereto sodium pyrophosphate and magnesium sulfate.

15. A stabilized bleach bath comprising unneutralized sodium peroxide,said bleach bath containing at least 0.75 pound of sodium peroxide per100 gallons of bleach liquor and also containing, as stabilizer for saidbath, sodium pyrophosphate and magnesium sulfate.

DONALD J. CAMPBELL. WILLIAM H. norms.

